Plastic encapsulated semiconductor devices having high lead counts or fine lead pitch are often times manufactured with a molded stiff carrier ring surrounding the package body of the device. The carrier ring supports the leads of the device for burn-in, test, probe, handling, and shipping purposes. Having the stiff carrier ring prevents damage, such as lead bending and lead skew, of the device during the aforementioned operations. When the device is ready to be mounted on a printed circuit board or a next level interconnect, the package body and the leads are excised from the carrier ring. The cut leads are then formed into a desired external lead configuration for mounting.
FIG. 1 illustrates a typical semiconductor device 10 as known in the prior art. Device 10 has a package body 12, a molded carrier ring 14, a plurality of leads 16 that extend from the package body 12 to the carrier ring 14, and a plurality of test contacts 17. Test contacts 17 are electrically interconnected to the leads 16, and thus allow testing of the device in the carrier ring. Occasionally, devices are tested by test probes contacting the leads 16 while they are still attached to the carrier ring.
Additionally illustrated in FIG. 1 is a molded gate 18 in a corner of the carrier ring, wherein the gate 18 extends from the inner corner of the carrier ring to a corner of the package body 12. The gate 18 serves as a conduit for the injection of resin from the carrier ring to the package body during a molding process. In a conventional mold, the resin compound is injected into a first cavity through a first gate (not illustrated) to form the carrier ring. After the resin compound fills the first cavity to form the carrier ring, the resin is fed from the first cavity through the gate 18 into a second cavity to form the package body 12.
FIG. 2 illustrates in detail the resin injecting area 22 of FIG. 1. The dotted line is used to indicate the metal leadframe underneath the molded gate 18. In the prior art, a slot 24 is designed into the leadframe to lock the gate 18 in place to prevent it from breaking away from the metal leadframe. The intent of the slot 24 in the prior art was to prevent premature breakage of the gate by interlocking of the top half of the gate to the bottom half of the gate on the underside of the leadframe. This feature is best understood by referring to FIG. 3 which illustrates a cross sectional view along line 3--3 of the gate 18 of FIG. 2. As shown, the large slot 24 in the leadframe 26 allows a joining and thus interlocking of the two halves of the gate. The corners 28 where the gate joins the package body 12 are the designated areas where the gate would break during a gate removal operation.
A gate removal operation typically precedes the package excising operation and the lead forming operation. One of the problems encountered by users of the semiconductor devices in a molded carrier ring is damage of formed leads during the operation of lead forming. Broken pieces of molded plastic can become embedded in the leads to cause misshapen formed leads or otherwise damage the plating on the leads. One source of the broken pieces of plastic is the molded gate during the gate removal operation because the gate breakage is typically not uniform or easily controlled. It would, thus, be desirable to be able to remove the gate without creating broken pieces of the plastic that could become embedded in the leads or the mechanical tooling associated with lead forming.